[Q] Can't downgrade modem

I have an i747m with a 4.3 bootloader. I rooted and installed custom recovery, and a 4.1.1 rom. But whenever I try to install a modem version lower than 4.3 i get a "no network" symbol. I have even tried wiping everything and using stock 4.1.1 odin images for the i747m but no luck. So far i have tried the following CWM flashable modems from this thread:
[MODEM] Complete Modem List for both I747U & I747M

XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality.Are you a developer?